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FencePlanner.pro ASTM Estimator & BOM
ASTM F537 Compliant
Preset: Western Red Cedar / Pine

Shadowbox (Board-on-Board) Fence Calculator

Alternating picket fence design that offers privacy while allowing wind passage through staggered gaps. Adjusted with ASTM post depth embedment and customizable waste buffers.

Project Dimensions & Specs

Customize measurements to automatically compute lumber breakdown

Real-Time Engine
100 ft
10 ft 250 ft 500 ft 1,000 ft
Estimated DIY Lumber Cost
$1,800 - $2,600 USD (Materials Only)
Informational Estimate Only: Regional lumber and concrete prices fluctuate weekly. Final material pricing, code compliance, and structural requirements must be verified with your local yard before ordering.
Item Specification Span / Dimensions Required Quantity
4x4x8' Pressure-Treated Timber
13 Line + 1 Terminal Post
 8' Spacing 14 pcs
2x4x8' Exterior Ground-Contact Rail
3 Rails Per Section + 10% Waste
 3 per section 43 pcs
1x6x6' Dog-Ear Exterior Board
219 Raw + 22 Waste Allowance
 5.5" Face / 0" Gap 241 pcs
Fast-Setting Concrete (50 lb)
Quikrete / Sakrete standard footing
 2 bags / hole 28 bags
Polymer Exterior Screws (2-1/2")
ACQ compatible rust-free coating
 ~3 Boxes (500ct) 1,446 pcs
Standard Post Hole Diameter: 10 to 12 inches
Min Embedment: 2.0 ft

Structural Elevation Preview

Live schematic rendering of posts, 2x4 rails, and picket alignment

Posts Rails Pickets
Grade / Soil Line

Contractor Field Guidelines for Shadowbox Fence Calculator

Engineering & ASTM Construction Standards

Structural rules for Western Red Cedar / Pine lumber longevity and load stability

1/3 In-Ground Post Depth Rule

Posts must be embedded to a minimum depth equal to 1/3 of the total timber length (or 1/2 the above-ground fence height). In cold climate zones, the post base must extend at least 6 inches below the local frost depth line.

2x4 Horizontal Rail Ratios

Use two horizontal rails for fences up to 4 feet tall. Fences 6 feet tall require three 2x4 rails to prevent cupping and warping. Fences 8 feet or taller require four rails to safely handle lateral wind pressure loads.

Fastener & Concrete Norms

Always anchor posts using two 50-lb bags of fast-setting concrete poured over a 4-to-6-inch base layer of tamped crushed gravel for drainage. Fasten pickets with two exterior ring-shank nails or polymer-coated screws per rail intersection.

Shadowbox Fence Calculator FAQs

Industry standard answers to common fence lumber calculations, post depth rules, and material questions.

What are the standard specifications for a shadowbox fence calculator?
A typical shadowbox fence calculator uses 6-foot finished height with 8-foot center-to-center post spacing. Pickets or infill slats generally measure 5.5 inches nominal width with a -1-inch gap.
How many posts do I need for a 100-foot fence?
For a straight 100-foot fence with standard 8-foot post spacing, you will need 14 posts (13 sections + 1 terminal end post). If you use 6-foot spacing for higher wind resistance, you will need 18 posts (17 sections + 1 terminal post).
How deep should fence posts be buried in the ground?
According to ASTM and standard building guidelines, a fence post must be buried to a depth equal to at least 1/3 of its total height. For example, a 6-foot tall fence requires an 8-foot post, with 2 feet buried below the surface. In cold climates, posts must extend below the local frost line to prevent frost heaving.
How many bags of concrete do I need per fence post?
A standard 4x4 wooden post set in a 10-inch to 12-inch diameter hole typically requires two 50-lb bags of fast-setting concrete. Taller fences (8 feet or higher) or heavy gate anchor posts generally require three 50-lb bags.
How many 2x4 rails are needed for a 6-foot privacy fence?
A 6-foot fence requires 3 horizontal 2x4 rails per section (top, middle, and bottom) to prevent vertical pickets from twisting or bowing under weather exposure. Fences 4 feet tall or shorter only require 2 rails.